Hmm interesting, I too have repaired many NES systems but the only thing I can think of that is causing this is a connection problem. What type of connection are you using to connect to your TV? I recommend a composite video cable, you can grab one for a buck on ebay. Other then that I would reccomend you take your NES apart make sure the 74 pin connector is solidly connected. I buy all my stuff from Nintendo repair shop, they have quality parts and they also have stuff to clean your games. So far I have not had a NES system or game that does not work. Way to go Nintendo for building solid machines.